Toward smooth MWPECVD diamond films: Exploring the limits of the hydrogen percentage in Ar/H2/CH4 gas mixture

► We explore the limits of the hydrogen percentage in Ar-H2-CH4 gas mixtures. ► We develop a new kind of buffer layer between the diamond films and treated silicon substrate. ► We obtain a low roughness of the coatings without modifying the Astex-type reactor.